Force cache reset as soon as the payload or a packet field is modified

[alxroyer-thales]

Brief description

When cache is set with a packet, modifying a value either in the payload or in a packet field does not reset the cache in the main packet.

This does not seem consistent with cache being reset on a final packet being modified.

Scapy version

2.6.1

Python version

3.8.6

Operating system

Windows

Additional environment information

No response

How to reproduce

Final packet modification:

class F(Packet):
    fields_desc = [
        ByteField("value", default=0),
    ]

f = F(bytes.fromhex("01"))
print(f"(before) f.raw_packet_cache={f.raw_packet_cache!r}")
f.value = 2
print(f"(after)  f.raw_packet_cache={f.raw_packet_cache!r}")

Output:

(before) f.raw_packet_cache=b'\x01'
(after)  f.raw_packet_cache=None

Cache is automatically reset.

Payload modification:

class M1(Packet):
    pass
bind_layers(M1, F)

m1 = M1(bytes.fromhex("01"))
print(f"(before) m1.raw_packet_cache={m1.raw_packet_cache!r}")
m1.value = 2
print(f"(after)  m1.raw_packet_cache={m1.raw_packet_cache!r}")

Output:

(before) m1.raw_packet_cache=b''
(after)  m1.raw_packet_cache=b''

Cache on the underlayer is unchanged.

Packet field modification:

class M2(Packet):
    fields_desc = [
        PacketField("f", pkt_cls=F, default=F()),
    ]

m2 = M2(bytes.fromhex("01"))
print(f"(before) m2.raw_packet_cache={m2.raw_packet_cache!r}")
m2.f.value = 2
print(f"(after)  m2.raw_packet_cache={m2.raw_packet_cache!r}")

Output:

(before) m2.raw_packet_cache=b'\x01'
(after)  m2.raw_packet_cache=b'\x01'

Cache on the parent packet is unchanged.

Actual result

Cache on underlayer and/or parent packets is unchanged.

Expected result

Cache of underlayer and parent packets should be automatically reset when a subpacket (either payload or packet field) is modified.

Related resources

No response

[alxroyer-thales]

See #4707 for an implementation proposal.